Class 73 Question

[ThePeakNed]

Evening all

Does anyone know if there are any physical differences between a JA 73 and a JB 73, or are the differences all internal workings?

 

[D7666]

Bogies.

Traction motors unless you want to count that one as internal.

 

[SuspectUsual]

Originally the JAs had oval buffers and the JBs round ones. They all ended up with round ones

 

[Islineclear3_1]

Apart from being built at different factories, didn't the JB's have one less cab mounted multiple unit jumper cable and one less bodyside window?

 

[eastwestdivide]

…didn't the JB's have one less cab mounted multiple unit jumper cable…

Definitely yes.

 

[Sun Chariot]

Apart from being built at different factories, didn't the JB's have one less cab mounted multiple unit jumper cable and one less bodyside window?

Correct.
The JA (73/0) was geared for 80mph.
The JB (73/1 and GatExp 73/2) was geared for 90mph, due to (as @D7666 states, above) different traction motors.

 

[Snow1964]

The six JAs were originally green,
I think the JBs were BR blue from introduction

 

[WarrenTManager]

The six JAs were originally green,
I think the JBs were BR blue from introduction

The JBs were initially outshopped in Electric Blue. I think deliveries finished in BR Blue. Not sure off the top of my head where the break point was. I'll have a book somewhere with it.

 

[wickham]

The technical opperating conditions were different for the two types - I believe the JAs could provide ETH off their diesel engines but the JBs could not. Also, don't think that JAs & JBs could work together in mu and I don't think the JAs could push-pull with EP family stock as the JBs could. Although completely "Southern" the JAs became non-standard against the larger JB class, hence their transfer to Merseyrail. It is a very long time since I was involved and memory fades, but perhaps someone can confirm or deny my points.

 

[norbitonflyer]

The technical opperating conditions were different for the two types - I believe the JAs could provide ETH off their diesel engines but the JBs could not. I don't think the JAs could push-pull with EP family stock as the JBs could.

I was told that that was why both a JA and a JB were needed on the Kenny Belle in winter when the coaching stock was a TC

 

[Sun Chariot]

I was told that that was why both a JA and a JB were needed on the Kenny Belle in winter when the coaching stock was a TC

I believe the JA and JB were MU-able. I've never got to the bottom of which EMUs linked up to the JA's extra high level MU. SUB? HAL?
The 73/0 (JA) could serve as a brake translator (vac-to-air / air-to-vac). The 73/1 etc (JB) could not

 

[43096]

The 73/0 (JA) could serve as a brake translator (vac-to-air / air-to-vac). The 73/1 etc (JB) could not

JBs can definitely do air-to-vac brake translation as evidenced at numerous heritage railway diesel galas over the years.

 

[Big Jumby 74]

Does anyone know if there are any physical differences between a JA 73 and a JB 73

Externally the bodyside grill/window arrangement differs slightly as well I believe.

 

[Wyrleybart]

The technical opperating conditions were different for the two types - I believe the JAs could provide ETH off their diesel engines but the JBs could not. Also, don't think that JAs & JBs could work together in mu and I don't think the JAs could push-pull with EP family stock as the JBs could. Although completely "Southern" the JAs became non-standard against the larger JB class, hence their transfer to Merseyrail. It is a very long time since I was involved and memory fades, but perhaps someone can confirm or deny my points.

Might be wrong but I think it was the other way round. Went on an Adex to Hastings back in the 1980s which was AC to Mitre Bridge Jn, then a Crompton to Eastbourne. 73004 (I think it was) backed on and the shunter coupled it up. When the driver got the tip from the guard and opened the power handle (on diesel) the engine shut down. Someone from the front vestibule ran up to the cab and told the driver to switch the heating off, which he did, and progress to Hastings was made.

I also vaguely remember a charter to the Severn Valley which I believe was a "JA + KB" combo - 73/0 and 33/1. I believe there was a complaint about lack of heat on the train, and I believe the driver got his manuals out where it stated you could not get ETH from this configuration.

 

[Sun Chariot]

JBs can definitely do air-to-vac brake translation as evidenced at numerous heritage railway diesel galas over the years.

Ah thanks. The web source I read (I can't find the darn site now), must be incorrect

 

[43096]

Might be wrong but I think it was the other way round. Went on an Adex to Hastings back in the 1980s which was AC to Mitre Bridge Jn, then a Crompton to Eastbourne. 73004 (I think it was) backed on and the shunter coupled it up. When the driver got the tip from the guard and opened the power handle (on diesel) the engine shut down. Someone from the front vestibule ran up to the cab and told the driver to switch the heating off, which he did, and progress to Hastings was made.

I think you’re both correct! As I understand it:
JA on diesel can either heat or provide traction power (but not both)
JB on diesel cannot heat at all

 

[WarrenTManager]

I think you’re both correct! As I understand it:
JA on diesel can either heat or provide traction power (but not both)
JB on diesel cannot heat at all

I thought this was the case 43096 as well.

 

[43096]

I thought this was the case 43096 as well.

I think of the JAs like a Class 31/4, you either get traction power or heat.

 

[Otis]

There appears to be some grill differences on the one side - both in terms of number of grills/windows and the spacings.

JA:



JB:



The other side (2x2 grill on the left) appears to be the same at first glance.

 

[ThePeakNed]

Externally the bodyside grill/window arrangement differs slightly as well I believe.

This is the answer I wanted...

However this thread has unlocked a lot of knowledge and for that I'm very grateful. Cheers all.

 

[SuspectUsual]

I think of the JAs like a Class 31/4, you either get traction power or heat.

 

[Wyrleybart]

I think of the JAs like a Class 31/4, you either get traction power or heat.

That is the biggest misnomer really.
The initial class 31s were fitted with ETH for a very specific reason which has probably been forgotten by many. They were London area "stock dodgers" used for taking trains of new electrically heated nay even air conditioned stock from the carriage sidings into the termini of Paddington, St Pancras and Kings Cross. They didn't need to be quick, but needed the then standard index of 66 to precondition the coaches for arrival at platforms. So look at the allocations of Old Oak, Cricklewood and Finsbury Park. They could deliver ETH and movement but a type two with 4 motors was never going to pack the speed punch, but could therm really well.